Increasingly high demands are being placed on internal combustion engines with regard to their performance and efficiency. At the same time, because of strict legal regulations, emissions must also be low. Such demands can readily be met if the internal combustion engine is fitted with gas-changing valves and corresponding actuators for said valves, in which the valve lift characteristic varies depending on the working point of the internal combustion engine. By this means, throttle losses upon intake of air can be reduced and high exhaust gas recirculation rates rapidly adjusted, where applicable.
It is known for the valve lift of a gas intake valve of the internal combustion engine to be adjusted between a low and a high valve lift. Thus, for example, the Porsche 911 Turbo is fitted with a device for adjusting the valve lift of the gas intake valve and of the gas outlet valve. The internal combustion engine of this vehicle is also equipped with a camshaft on which for each gas intake valve one cam with a low lift and two further cams with a higher lift are fashioned. The cam lift is transferred by means of a transfer unit to the gas intake valve. The transfer unit is fashioned as a cup tappet which comprises a cylinder element and an annular cylinder element arranged concentrically in relation to said cylinder element. The cam having a low lift acts upon the cylinder element while the cams having the higher lift act upon the annular cylinder element. Depending on a switching position of the cup tappet, either the low lift or the higher lift is transferred to the gas intake valve. When the internal combustion engine is idling, the low cam lift is transferred to the gas intake valve. Reduced frictional losses are produced by this means due to the small diameter of the cam used in this operating state and to the cylinder element and to the lower valve lift.
A higher load movement is also achieved. In this way, the emissions of the internal combustion engine can be reduced and fuel consumption kept low at the same time. The small valve lift is retained for low and moderate loads. Throttle losses can additionally be reduced by means of an appropriate phase adjustment between the gas intake valve and the gas exhaust valve and a resulting internal exhaust gas recirculation rate. When the load demands on the internal combustion engine are high, it switches over to the higher valve lift.
For a high level of driving comfort in a vehicle in which an internal combustion engine of this type is arranged, it is important to ensure that running irregularities in the internal combustion engine are low. This is a major challenge particularly at working points at which some of the gas intake valves are being operated with a high valve lift and others with a low valve lift.
From EP 1 323 902 A2 a method for controlling an internal combustion engine is known which comprises a variable valve timing control device for the gas intake valves. A target opening timing for a gas intake valve is determined. An actual opening timing for the gas intake valve is also determined. An ignition angle is corrected depending on a deviation between the target value and the actual value for the opening timing of the gas intake valve.